How do I start an Intent from an OnClickListener

Question

My Main Activity extends ListActivity and displays a List. I am using custom Listitems defined in a class named DefinitionAdapter. I also have a seperate class that implements OnClickListener.

In the class DefinitionAdapter I set the OnClickListener to the ListItems:

   public View getView(int position, View convertView, ViewGroup parent) {
        View v = convertView;
        if (v == null) {
            LayoutInflater vi = (LayoutInflater)getContext().getSystemService(
                    Context.LAYOUT_INFLATER_SERVICE);
            v = vi.inflate(R.layout.row, null);
        }
...

        v.setOnClickListener(new OnItemClickListener(position) );

        return v;
   }

My custom OnClickListener is supposed to start another activity.

public class OnItemClickListener implements OnClickListener extends Activity {


    private int position;

    public OnItemClickListener(int p) {

        position = p;   
    }

    @Override
    public void onClick(View v) {

        Intent intent = new Intent(this, ShowDefinition.class);
        startActivity(intent);

    }

}

I am not sure that I am doing that right. I added my new activity to the manifest, as well as the activity i extended the listener with:

<activity android:name="ShowDefinition" android:label="@string/app_name">
</activity>
<activity android:name="OnItemClickListener" android:label="@string/app_name">
</activity>

Nonetheless, if I click on an Item in my List, the application always breaks with a NullPointerException. I think I am using the intent wrong... any Ideas?

In regard to Nikita Beloglazov's comment:

It breaks when I create the Intent:

Intent intent = new Intent(this, ShowDefinition.class);

Here's the stacktrace:

05-23 22:56:46.629: ERROR/AndroidRuntime(258): Uncaught handler: thread main exiting due to uncaught exception
05-23 22:56:46.659: ERROR/AndroidRuntime(258): java.lang.NullPointerException
05-23 22:56:46.659: ERROR/AndroidRuntime(258):     at android.content.ContextWrapper.getPackageName(ContextWrapper.java:120)
05-23 22:56:46.659: ERROR/AndroidRuntime(258):     at android.content.ComponentName.<init>(ComponentName.java:75)
05-23 22:56:46.659: ERROR/AndroidRuntime(258):     at android.content.Intent.<init>(Intent.java:2551)
05-23 22:56:46.659: ERROR/AndroidRuntime(258):     at com.andiandy.juradefinitions.OnItemClickListener.onClick(OnItemClickListener.java:22)
05-23 22:56:46.659: ERROR/AndroidRuntime(258):     at android.view.View.performClick(View.java:2364)
05-23 22:56:46.659: ERROR/AndroidRuntime(258):     at android.view.View.onTouchEvent(View.java:4179)
05-23 22:56:46.659: ERROR/AndroidRuntime(258):     at android.view.View.dispatchTouchEvent(View.java:3709)
05-23 22:56:46.659: ERROR/AndroidRuntime(258):     at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:852)
05-23 22:56:46.659: ERROR/AndroidRuntime(258):     at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:884)
05-23 22:56:46.659: ERROR/AndroidRuntime(258):     at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:884)
05-23 22:56:46.659: ERROR/AndroidRuntime(258):     at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:884)
05-23 22:56:46.659: ERROR/AndroidRuntime(258):     at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:884)
05-23 22:56:46.659: ERROR/AndroidRuntime(258):     at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:884)
05-23 22:56:46.659: ERROR/AndroidRuntime(258):     at com.android.internal.policy.impl.PhoneWindow$DecorView.superDispatchTouchEvent(PhoneWindow.java:1659)
05-23 22:56:46.659: ERROR/AndroidRuntime(258):     at com.android.internal.policy.impl.PhoneWindow.superDispatchTouchEvent(PhoneWindow.java:1107)
05-23 22:56:46.659: ERROR/AndroidRuntime(258):     at android.app.Activity.dispatchTouchEvent(Activity.java:2061)
05-23 22:56:46.659: ERROR/AndroidRuntime(258):     at com.android.internal.policy.impl.PhoneWindow$DecorView.dispatchTouchEvent(PhoneWindow.java:1643)
05-23 22:56:46.659: ERROR/AndroidRuntime(258):     at android.view.ViewRoot.handleMessage(ViewRoot.java:1691)
05-23 22:56:46.659: ERROR/AndroidRuntime(258):     at android.os.Handler.dispatchMessage(Handler.java:99)
05-23 22:56:46.659: ERROR/AndroidRuntime(258):     at android.os.Looper.loop(Looper.java:123)
05-23 22:56:46.659: ERROR/AndroidRuntime(258):     at android.app.ActivityThread.main(ActivityThread.java:4363)
05-23 22:56:46.659: ERROR/AndroidRuntime(258):     at java.lang.reflect.Method.invokeNative(Native Method)
05-23 22:56:46.659: ERROR/AndroidRuntime(258):     at java.lang.reflect.Method.invoke(Method.java:521)
05-23 22:56:46.659: ERROR/AndroidRuntime(258):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:860)
05-23 22:56:46.659: ERROR/AndroidRuntime(258):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:618)
05-23 22:56:46.659: ERROR/AndroidRuntime(258):     at dalvik.system.NativeStart.main(Native Method)

At what line if breaks exactly? Could you post stacktrace? – Mikita Belahlazau May 23 '11 at 23:03 — Mikita Belahlazau, May 23 '11 at 23:03

score 22 · Accepted Answer · answered May 23 '11 at 23:08

22

Your OnItemClickListener should not extend Activity. Instead, you should arrange for the OnItemClickListener to have access to your ListActivity instance. Any view that is already part of the activity (like the ListView) has access to the ListActivity instance via getContext(). Then implement onClick like this:

@Override
public void onClick(View v) {
    Intent intent = new Intent(context, ShowDefinition.class);
    context.startActivity(intent);
}

answered May 23 '11 at 23:08

Ted Hopp

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8

That actually does the trick. I already tried: `Intent intent = new Intent(v.getContext(), ShowDefinition.class);` But then I startet the intent with startActivit(intent). Now I use `v.getContext().startActivity(intent)` that does the trick. Thanks! – AndiH May 23 '11 at 23:20
Glad it worked. A much better approach, actually, is to override `onListItemClicked` in your ListActivity subclass. Then you don't need any click listeners. (P.S. If you haven't done it yet, don't forget to remove OnItemClickListener from the list of activities in the manifest.) – Ted Hopp May 23 '11 at 23:28
I just did so, following I_Artist's instructions. This is really much better. I guess I just didn't find the right ListActivity instructions. Should have read the documentation more carefully. Thanks for the help. – AndiH May 23 '11 at 23:41
@twittfort thanks!, it works fine when list view displayed, when I integrate search filter to custom array adapter, after search result displayed( notifyDataSetChanged();) on list view when I click on item it crashes while calling Intent, any solution for that? – LOG_TAG Jan 14 '13 at 04:30

MikeWallaceDev · Answer 2 · 2011-05-23T23:40:57.287

There are two ways to implement an onItemClickListener. You don't need to create a new class. Maybe you can try it the easy way for now :)

Have your ListActivity implement AdapterView.OnItemClickListener

public class MyActivity extends ListActivity implements AdapterView.OnItemClickListener

Then in your ListActivity's onCreate set your onClickListener like this :

        ListView lstvwContacts = getListView();
        lstvwContacts.setOnItemClickListener(this);

And then you can react to the click like this :

public void onItemClick(AdapterView<?> parent, View v, int position, long id) {
    switch (parent.getId()) {
        case android.R.id.list: {
            Log.v(TAG, "onItemClick");
            Intent intent = new Intent(this, ShowDefinition.class);
            startActivity(intent);
        }    
    }
}

That should do it for clicks. If you need to know when an item is selected you can look into AdapterView.OnItemSelectedListener

-I_Artist

Thanks. I'll apreciate that solution. I will try to implement it that way in the future. I made the extra class for easier understanding of the concept. — AndiH, May 23 '11 at 23:25
Okay, now I tried your solution. It really is much simpler! I just had trouble with implementing AdapterView.OnItemClickListener. Eclipse didn't find it. I had to implement android.widget.AdapterView.OnItemClickListener — AndiH, May 23 '11 at 23:40

score 0 · Answer 3 · answered May 23 '11 at 23:10

Your conception is wrong, your OnItemClickListener shouldn't extends Activity and you should n't build a new onClickListener each time.

public class MainActivity extends Activity {
    OnItemClickListener = null;

   MainActivity() {
    //Build your OnItemClickListener with a valid context
    OnItemClickListener = new OnItemClickListener(this);
   }

   public View getView(int position, View convertView, ViewGroup parent) {
   ...

   //Here user the OnItemClickListener

   }
}

How do I start an Intent from an OnClickListener

3 Answers3

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